Fiber cord for reinforcement and method for producing the same

ABSTRACT

A fiber cord for reinforcement has an adhesive treatment agent attached to a surface thereof and includes, in an inner layer part thereof, two kinds of compounds each having a molecular weight of less than 1,000. The main compound is an aromatic compound or contains an α-dicarboxylic acid component, and the other compound is an aliphatic compound or an alicyclic compound. It is preferable that the adhesive treatment agent is a resorcin-formalin- latex-based adhesive, that the fiber cord includes a twisted synthetic fiber, that the aromatic compound is a heterocyclic compound, that the main compound is located only in the inner layer part of the fiber cord, that a compound having a hexamethylene diisocyanate trimer structure is present, and that no latex is present in the inner layer part of the fiber cord. This fiber cord is produced through a two-stage treatment with a pre-treatment liquid and adhesive treatment liquid.

TECHNICAL FIELD

The present invention relates to a fiber cord for reinforcement. It morespecifically relates to a fiber cord for reinforcement havingsignificantly improved fraying resistance, and also to a method forproducing the same.

BACKGROUND ART

In recent years, to deal with the global environmental destruction,petroleum resource depletion, and like problems, a great amount ofattention has been paid to energy saving and energy substitution forautomobiles, electric appliances, etc. In particular, with automotiveweight reduction for improving the fuel efficiency, the need for theweight and size reduction of components is rapidly increasing. As suchcomponents, fiber-reinforced composite materials have been widely used.

However, such composite materials containing fibers for reinforcementhave the problem that when the material is once shaped and then cut, thefibers are frayed at the cut face. This phenomenon is especiallyprominent in fiber-reinforced rubber composite materials such as belts.Because the rubber forming the matrix of the composite is prone todeformation, high-strength fibers for reinforcement, which hardly followthe deformation, are exposed at the end face of the composite material,and this is likely to cause the problematic fraying.

As one technique for reducing such fraying, a method that treats a fiberwith a solvent-based adhesive is known (e.g., PTL 1 and PTL 2). However,such organic-solvent-based adhesive treatments have problems in that aheavy load is placed on the safety or working environment, and also thecosts for adhesive treatment facilities, recovery/waste liquid disposal,and peripheral facilities thereof are extremely high.

Thus, in order to deal with the above problems, a method for producingan adhesive-treated fiber using a water-based adhesive has been tried.For example, PTL 3 proposes a fiber cord for reinforcement, in which afirst layer of the fiber cord is treated with a water-based adhesiveincluding a water-based urethane resin, an epoxy compound, a blockedpolyisocyanate, and a rubber latex, and a second layer is treated with aresorcin-formalin-latex (RFL)-based adhesive.

However, with these water-based techniques, under the presentcircumstances, the high-level adhesion, fraying resistance, and fatigueresistance required for automotive transmission belts, etc., have notbeen achieved to the levels of solvent-based techniques.

PTL 1: JP-A-9-158989

PTL 2: JP-A-11-81152

PTL 3: JP-A-2003-221787

SUMMARY OF THE INVENTION Technical Problem

The invention has been accomplished in view of the above backgroundproblems and art. An object of the invention is to provide a fiber cordfor reinforcement having significantly improved fraying resistance andbeing excellent in adhesion to the matrix and fatigue resistance(durability), and also a method for producing the same.

Solution to Problem

The fiber cord for reinforcement of the invention is a fiber cord forreinforcement having an adhesive treatment agent attached to the surfacethereof, characterized in that the fiber cord includes, in an innerlayer part thereof, a compound A₁ having a molecular weight of less than1,000 and a smaller amount of a compound B₁ than the compound A₁, thecompound A₁ being an aromatic compound or a compound containing anα-dicarboxylic acid component, the compound B₁ being an aliphaticcompound or an alicyclic compound.

Further, it is preferable that the adhesive treatment agent is aresorcin-formalin-latex (RFL)-based adhesive, the fiber cord includes atwisted multifilament fiber or a synthetic fiber, and the aromaticcompound is a heterocyclic compound. In addition, it is preferable thatthe compound A₁ is located only in the inner layer part of the fibercord, a compound having a hexamethylene diisocyanate (HDI) trimerstructure is present in the inner layer part of the fiber cord, and nolatex is present in the inner layer part of the fiber cord.

In addition, the method for producing a fiber cord for reinforcement ofthe invention is a method for producing a fiber cord for reinforcement,including treating a fiber cord in two stages with a pre-treatmentliquid and an adhesive treatment liquid. The method is characterized inthat the pre-treatment liquid contains two kinds of blocked isocyanatecompounds that are a compound A₂ and a smaller amount of a compound B₂,the compound A₂ having an isocyanate group blocked with an aromaticcompound or a compound containing an α-dicarboxylic acid component, thecompound B₂ having an isocyanate group blocked with an aliphaticcompound or an alicyclic compound, and a fiber cord having thepre-treatment liquid attached thereto is once subjected to a heattreatment, and then the adhesive treatment liquid is attached thereto,followed by a drying treatment.

Further, it is preferable that the aromatic compound is a heterocycliccompound, and the unblocking temperature of the compound A₂ is lowerthan the unblocking temperature of the compound B₂. In addition, it ispreferable that the compound A₂ has a hexamethylene diisocyanate (HDI)trimer structure, and the compound B₂ has an isocyanate group blockedwith an aliphatic compound or an alicyclic compound.

Advantageous Effects of the Invention

According to the invention, a fiber cord for reinforcement havingsignificantly improved fraying resistance and being excellent inadhesion to the matrix and fatigue resistance (durability) and a methodfor producing the same are provided.

DESCRIPTION OF EMBODIMENTS

The fiber cord for reinforcement of the invention has an adhesivetreatment agent attached to the surface thereof. The adhesive treatmentagent herein is not particularly limited and selected from thosesuitable for a structure (matrix) to be reinforced with fibers. However,more specifically, for example, in the case where the matrix is a rubberor the like, it is preferable that the adhesive treatment agent is aresorcin-formalin-latex (RFL)-based adhesive.

Then, the fiber forming the fiber cord for reinforcement used in theinvention is in a fibrous form to reinforce the matrix of the structure,and it is preferable that this fiber is a synthetic fiber. Morespecifically, for example, it is preferable that the fiber is asynthetic fiber made of at least one kind of synthetic resin selectedfrom polyesters, polyarylates, aliphatic polyamides, vinylon, whollyaromatic polyamides, polyparabenzobisoxazole, and carbon fibers. Amongthem, organic fibers are preferable, and polyester fibers and whollyaromatic polyamide fibers are particularly preferable. Examples ofpreferred polyester fibers include a polyethylene terephthalate fiber, apolybutylene terephthalate fiber, and a polyethylene-2,6-naphthalatefiber. Examples of preferred wholly aromatic polyamide fibers includewholly aromatic para-type polyamide fibers and meta-type polyamidefibers. However, in terms of reinforcement, high-strength para-typearomatic polyamide fibers are preferable. In addition, in terms of thebalance between strength and adhesion, further, it is preferable thatthe fiber forming the fiber cord is at least one kind of polyester fiberselected from polyethylene terephthalate, polyethylene-2,6-naphthalate,and the like.

As the applications of the fiber cord for reinforcement of theinvention, it is preferable that the fiber cord is used as a rubberfiber composite, particularly a cord of a rubber belt. In particular, inthe case where the fiber cord is used as a belt cord, the use of theabove fiber makes the fiber cord more optimal in terms of tensilestrength performance, dimensional stability, durability, and generalversatility.

Here, it is preferable that the fiber cord for reinforcement of theinvention is a single yarn or an assembly of several yarns. Then, it isalso preferable that a single yarn forming the fiber cord forreinforcement itself is an assembly of several fiber filaments in theform of a bundle. It is preferable that the fineness of the single yarn(assembly of fiber filaments) is 500 to 4,000 dtex, still morepreferably 1,000 to 3,000 dtex. Such a yarn is particularly effective interms of handle ability in the steps of twisting, adhesive treatment,and shaping. It is preferable that the total fineness of the fiber cordfor reinforcement of the invention, which is an assembly of such yarns,is 500 to 15,000 dtex. Incidentally, no particular limitations areimposed on the number of filaments of the fiber, its cross-sectionalshape, the physical properties of the fiber, the microstructure, thepolymer properties (molecular weight, terminal functional groupconcentration, etc.), additives in the polymer, etc. In addition, it isalso preferable that the fiber yarn has been previously pre-treated withan epoxy resin, a urethane resin, or the like in the stage ofyarn-making or after yarn making.

The fiber cord for reinforcement used in the invention is an assembly ofone or more such yarns, and it is still more preferable that it is atwisted cord. Further, it is preferable that the fiber cord is obtainedby aligning and twisting one or more such yarns (first twisting) andthen aligning and twisting two or more such twisted yarns (secondtwisting). Twisting particularly improves the bending fatigue resistanceand the like. Here, it is preferable that the number of twistsrepresented by the following equation (1) is within a range such thatthe twist coefficient K satisfies 300 to 1,200, more preferably K=500 to1,000. When such a number of twists is satisfied, the bending fatigueresistance is satisfied while maintaining the penetration of theadhesive into the fiber cord to exert fraying resistance.

[Equation 1]

K=T×√D   (1)

(wherein K: twist coefficient, T: the number of twists per m [twists/m],D: total fineness [dtex])

When the twist coefficient K is less than 300, the bending fatigueresistance and adhesion tend to decrease. Meanwhile, in the case where Kis more than 1,200, there is a tendency that the strength decreases, andalso the treatment agent (first adhesive treatment agent) is unlikely tosufficiently penetrate into the fiber cord, resulting in a decrease infraying resistance.

Incidentally, in the case where the fiber cord for reinforcement of theinvention is obtained by aligning and twisting one or more fiber yarns(first twisting) and then aligning and twisting two or more such twistedyarns (second twisting) as described above, it is preferable that thefirst twisting and second twisting both satisfy the twist coefficientK=300 to 1,200, and the twist coefficients of the first twisting and thesecond twisting may be the same or different.

The fiber cord for reinforcement of the invention is a fiber cord forreinforcement having an adhesive treatment agent attached to the surfaceof such a fiber cord. Then, the fiber cord includes, in the inner layerpart thereof, a compound A₁ having a molecular weight of less than 1,000and a smaller amount of a compound B₁ than the compound A₁. Here, thecompound A₁ is an aromatic compound or a compound containing anα-dicarboxylic acid component, and the compound B₁ is an aliphaticcompound or an alicyclic compound. Here, it is preferable that thecompound B₁ is a compound other than the compound A₁, which isstructurally different from the compound A₁. More specifically, it ispreferable that the compound B₁ is a compound that does not contain anaromatic compound or an α-dicarboxylic acid component.

Here, the compound A₁ present in the inner layer part of the fiber cordof the invention is a compound having a molecular weight of less than1,000, and is an aromatic compound or a compound containing anα-dicarboxylic acid component. Such compounds are structurally prone toresonance because of the presence of a double bond. In addition, here,aromatic compounds are not limited to ordinary aromatic compoundscomposed only of carbon atoms. Heterocyclic compounds having a cyclicstructure formed by nitrogen or like atoms in addition to carbon andhaving aromatic properties, that is, heterocyclic aromatic compounds,are also preferable. Specific examples of compounds particularlypreferable as the compound A₁ include phenols such as phenol,thiophenol, cresol, and resorcinol, aromatic secondary amines such asdiphenylamine and xylidine, heterocyclic compounds such asdimethylpyrazole, and α-dicarboxylic acids such as diethyl malonic acid.Among them, dimethylpyrazole, which is a heterocyclic aromatic compound,is particularly preferable.

In addition, the compound B₁ present inside the fiber cord in an amountsmaller than that of the compound A₁ (weight ratio) is an aliphaticcompound or alicyclic compound having no aromatic properties. Suchcompounds B₁ are ordinary compounds that do not have a resonancestructure like the compound A₁. In addition, with respect to themolecular weight of the compound B₁, similarly to the compound A₁, acompound having a molecular weight of less than 1,000 is preferable.More specifically, examples of compounds particularly preferable as thecompound B₁ include phthalic imides, lactams such as caprolactam andvalerolactam, oximes such as methylethylketoxime, and aliphaticcompounds such as acidic sodium sulfite. Among them, ε-caprolactam,which is a lactam, is particularly preferable. Further, in the casewhere dimethylpyrazole is used as the compound A₁, when a lactam iscombined therewith as the compound B₁, the impregnation of the agentinto the fiber is excellent, and the performance of the fiber cord isparticularly improved.

In the inner layer part of the fiber cord for reinforcement of theinvention, the compounds A₁ and B₁ each having a molecular weight ofless than 1,000 as described above are contained, and further it ispreferable that the molecular weights of these compounds are each 60 ormore and less than 600.

In addition, it is necessary that the content of the compound A₁ in thefiber cord inner layer part is higher than the content of the compoundB₁ (weight ratio), and further it is preferable that the abundance ratiobetween the compound A₁ and the compound B₁ (weight ratio), A₁/B₁ ratio,is within a range of 60/40 to 95/5.

Here, when the solids weight ratio of compound A₁/compound B₂ isincreased, the film formation inside the fiber bundle tends to takeplace more effectively. Thus, a firm film is formed, and, when the fibercord of the invention is eventually used for a composite, improvedfraying resistance is provided. This attributes to the fact that thecompound A₁, which is a compound prone to having a resonance structure,has high reactivity and is effective in film formation. That is,specifically, it is preferable that the abundance ratio of A₁/B₁ is atleast 60/40. Meanwhile, in the case where the solids weight ratio ofcompound A₁/compound B₂ is too high, there is a tendency that the filminside the fiber is likely to be hard and brittle, and the bendingfatigue resistance and durability tend to decrease. It is preferablethat the solids weight ratio of compound A₁/compound B₂ is 95/5 or less.It is preferable that such compounds A₁ and B₁ are attached in an amountwithin a range of 0.0001 to 0.2 wt % relative to the fiber.

In addition, in the inner layer part of the fiber cord for reinforcementof the invention, in addition to these relatively low-molecularcompounds, it is preferable that high-molecular compounds derived fromepoxy compounds and the like are also present. Further, with respect tothe compounds A₁and B₁ present inside the fiber bundle, it is preferablethat the total amount thereof attached is within a range of 0.01 wt % to2 wt % relative to the amount (weight) of other components attached tothe fiber, such as high-molecular compounds. When such high-molecularcompounds, that is, resin-like substances, are present in large amountsin the inner layer of the fiber bundle, high bundling properties can beobtained. When the abundances of the compounds A₁ and B₁ are too high,conversely, the adhesion to the matrix tends to decrease, while when theabundances are too low, there is a tendency that the fiber cord isdifficult to bundle, resulting in a decrease in fraying resistance.

Here, as high-molecular compounds present in the fiber bundle innerlayer of the invention, epoxy compounds, latex rubbers, and the like arepreferable. As epoxy compounds, it is preferable that an epoxy compoundhaving an epoxy group is attached to the fiber surface, followed by aheat treatment or the like to increase the molecular weight. Specificexamples thereof include reaction products between a polyalcohol such asethylene glycol, glycerol, sorbitol, pentaerythritol, or polyethyleneglycol and a halogen-containing epoxide such as epichlorohydrin;reaction products between a polyphenol such as resorcin,bis(4-hydroxyphenyl)dimethylmethane, a phenol-formaldehyde resin, or aresorcin-formaldehyde resin and a halogen-containing epoxide asdescribed above; and polyepoxide compounds prepared by oxidizing anunsaturated compound with peracetic acid, hydrogen peroxide, or thelike, that is, 3,4-epoxycyclohexene epoxide,3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexene carboxylate, bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate, and the like. Among them,a reaction product between a polyalcohol and epichlorohydrin, that is, apolyglycidyl ether compound of a polyalcohol, develops excellentperformance and thus is particularly preferable. It is preferable thatthe ratio between the epoxy compound and the total amount of thecompounds A₁ and B₁ (epoxy compound)/(compound A₁+compound B₁) is withina range of 1/2 to 6/1.

Further, in order to facilitate adhesion to the surface adhesive layeror to the matrix component of the final composite material, it ispreferable that an isocyanate component is contained in the inner layerof the fiber cord. In particular, in order to suppress deactivationduring the process, it is preferable that an isocyanate componentderived from a blocked polyisocyanate compound is contained.

Further, in the invention, it is preferable that the isocyanatecomponent is derived from a compound having a hexamethylene diisocyanate(HDI) trimer structure represented by the following chemical structuralformula (I).

As shown in the above chemical structural formula (I), this compound isa compound having, as its basic structure, a trimer structure in whichthree terminal NCO groups of the hexamethylene diisocyanate (HDI) form acyclic structure. Further, as each trimer structure, as shown in thefollowing chemical structural formula (II), for example, a compoundcondensed to further increase the functionality is also preferable.Here, R of chemical structural formula (II) can be selected frompolyglycols, such as polyethylene glycol, without impairing the affinityfor water and heat resistance.

In addition, as the isocyanate component, it is preferable that thenumber of NCO functional groups present in the molecule is three ormore, whereby the adhesion can be further improved.

As other isocyanate components, components derived from adiphenylmethane diisocyanate (MDI) compound are preferable. Componentsderived from a compound having a hexamethylene diisocyanate (HDI) trimerstructure described above are flexible, while components derived from adiphenylmethane diisocyanate (MDI) compound are rigid. Accordingly, whenthese two kinds of components are present together, a film that is firm,dense, and also flexible is formed in the inner layer part of the fibercord. Then, the fiber cord for reinforcement of the invention allows formore significant improvements in, in addition to fraying resistance,bending fatigue resistance and adhesion.

In the fiber cord for reinforcement of the invention, as describedabove, the compound A₁ and the compound B₁ are contained in the innerlayer part of the fiber cord, and the surface of the fiber cord hasattached thereto an adhesive treatment agent. Here, the adhesivetreatment agent can be suitably changed according to the object to bereinforced with the fiber cord. Among them, particularly in the casewhere the fiber cord of the invention is used to reinforce a rubberproduct such as a belt, it is preferable to use aresorcin-formalin-latex (RFL)-based adhesive as the adhesive treatmentagent.

Here, RFL-based adhesives preferable to use will be described. It ispreferable that the molar ratio between resorcin and formaldehyde in theresorcin-formalin-rubber latex (RFL) is within a range of 1/0.6 to 1/8,more preferably within a range of 1/0.8 to 1/6. When the amount offormaldehyde added is too small, the crosslinking density of theresorcin-formalin condensate decreases, and the molecular weight alsodecreases. Accordingly, the cohesive strength of the adhesive layer maydecrease, resulting in a decrease in adhesion and also a decrease inbending fatigue resistance. In addition, on the other hand, when theamount of formaldehyde added is too large, the resorcin-formalincondensate tends to be hard due to an increase in crosslinking density.Then, at the time of covulcanization with the adherend rubber, thecompatibilization between RFL and the rubber maybe inhibited, resultingin a decrease in the adhesion of the fiber cord for reinforcement.

In addition, with respect to the blending ratio betweenresorcin-formalin (RF) and latex (L) in this adhesive, the RF/L solidsweight ratio is 1/3 to 1/16, more preferably 1/4 to 1/10. When theproportion of the rubber latex is too low, the amount of components tobe covulcanized with a rubber is small, and thus the adhesion strengthis likely to decrease. On the other hand, when the proportion of therubber latex is too high, it becomes difficult to obtain sufficientstrength as an adhesive film. Further, the adhesion strength anddurability tend to decrease, and also the stickiness of theadhesive-treated fiber cord tends to be too high. Accordingly,gumming-up, handle ability deterioration, or the like may occur in theadhesive treatment step or shaping step, resulting in a decrease inprocess-passing properties.

Further, as the latex forming the RFL-based adhesive, various latexessuch as vinyl pyridine-styrene-butadiene (VpSBR) latex, chlorosulfonatedpolyethylene (CSM) latex, and polybutadiene (PB) latex are usable. It isparticularly preferable that the latex includes VpSBR latex and/or CSMlatex and PB latex. In addition, with respect to their solids weightratio, defining the total weight of “VpSBR latex and/or CSM latex” as L₁and the weight of “PB latex” as L₂, it is preferable that the L₁/L₂ratio is within a range of 25/75 to 75/25.

It is optimal to use the above latexes particularly in the case wherethe fiber cord for reinforcement of the invention is used, among rubberreinforcement applications, particularly for a transmission belt.Usually, in a compressed rubber layer of a transmission belt, alow-adhesion, high-performance synthetic rubber, such asethylene-α-olefin-diene rubber, chloroprene rubber, hydrogenated nitrilerubber, chlorosulfonated polyethylene rubber, or styrene-butadienerubber, is used. In contrast, the fiber cord for reinforcement of theinvention employs the above composition and compositional proportions,and thus has high affinity and covulcanizability. In the invention, itis important to have high affinities both for the polymer forming thefiber cord and for other agents, and it has become possible to improvethe fraying resistance, bending fatigue resistance, and adhesion athigher levels.

It is preferable that the solids weight ratio of L₁/L₂ in the fiber cordof the invention is within a range of 25/75 to 75/25 as described above.Further, it is more preferable that the solids weight ratio of L₁/L₂ is30/70 to 70/30. In the case where L₁ is too low, the affinities for thepolymer forming the fiber cord and for the rubber forming thetransmission belt decrease. Accordingly, the adhesion strength tends todecrease, and the bending fatigue resistance and adhesion of the finalproduct also tend to decrease. Meanwhile, in the case where L₁ is toolarge, the unsaturated bonding of the latex in the adhesive treatmentagent is reduced. Accordingly, there is a tendency that thecovulcanizability with the rubber forming the transmission beltdecreases, resulting in decreases in bending fatigue resistance andadhesion.

Examples of resorcin compounds used for the adhesive treatment agentinclude pre-oligomerized resorcin-formalin initial condensates andpolynuclear chlorophenol-based resorcin-formalin initial condensatesprepared by oligomerizing chlorophenol, resorcin, and formalin. They maybe used alone or in combination as necessary.

In addition, it is also preferable that a crosslinking agent is usedtogether with this adhesive treatment agent. Examples of preferredcrosslinking agents to be added include amines, ethylene urea, andblocked polyisocyanate compounds. Considering the temporal stability ofthe treatment agent, the interaction with the pre-treatment agent, andthe like, it is preferable to use a blocked polyisocyanate compound.

It is preferable that the proportion of a crosslinking agent, such as ablocked polyisocyanate, added to this adhesive treatment agent is withina range of 0.5 to 40 wt %, preferably 10 to 30 wt %, relative to theresorcin-formalin-rubber latex (RFL). An increase in the amount addedusually improves the adhesion strength. Meanwhile, when the amount addedis too large, conversely, there is a tendency that the compatibility ofthe adhesive with rubbers decreases, resulting in a decrease in adhesionstrength to rubbers.

Further, it is preferable that the fiber cord for reinforcement of theinvention does not contain an organic solvent. When an organic solventis not contained, the environment is not adversely affected, and it hasalso become possible to prevent the degradation of performance withtime. Such a fiber cord for reinforcement can be obtained using, forexample, not an organic-solvent-based treatment liquid but a water-basedtreatment liquid.

Like this, in the fiber cord for reinforcement of the invention, theadhesive treatment agent is attached to the surface of the fiber cord,and the compound A₁ and the compound B₁ are contained in the inner layerpart of the fiber cord. Then, in the fiber cord for reinforcement of theinvention, it is preferable that the compound A₁ is not present in thesurface of the fiber cord, but is located only in the inner layer partof the fiber cor. When the compound A₁ is located only in the fiber cordinner layer part, there is a tendency that the adhesion inside the fibercord is improved, whereby the bundling properties are likely to befurther improved. This effect is particularly prominent in the casewhere an epoxy compound is present inside the fiber bundle, which isconsidered to be attributable to the affinity between the epoxy compoundand the compound A₁. In addition, it is preferable that a compoundhaving a hexamethylene diisocyanate (HDI) trimer structure is present inthe inner layer part of the fiber cord, and no latex is present in theinner layer part of the fiber cord. The presence of a latex in the fibercord inner layer part inhibits the affinity between the compound A₁ andepoxy and thus is undesirable. In addition, it is preferable that thecompound B₁ is unevenly located in the fiber cord inner layer part. Thisis because the presence of the compound B₁ weakens the interactionbetween the latex and the compound A₁. In the invention, because of sucha configuration of the inner layer part, moderate joining can bemaintained between fiber filaments in the fiber cord inner layer, andfurther the fraying resistance can be improved.

In addition, such a fiber cord for reinforcement of the invention can beobtained by a method for producing a fiber cord for reinforcement, whichis another embodiment of the invention. That is, the fiber cord forreinforcement of the invention can be obtained by a method for producinga fiber cord for reinforcement, including treating a fiber cord in twostages with a pre-treatment liquid and an adhesive treatment liquid. Thepre-treatment liquid contains two kinds of blocked isocyanate compounds,that is, a compound A₂ and a smaller amount of a blocked isocyanatecompound B₂. The compound A₂ has an isocyanate group blocked with anaromatic compound or a compound containing an α-dicarboxylic acidcomponent, and the compound B₂ has an isocyanate group blocked with analiphatic compound or an alicyclic compound. A fiber cord having thepre-treatment liquid attached thereto is once subjected to a heattreatment, and then the adhesive treatment liquid is attached thereto,followed by a drying treatment.

The fiber forming the fiber cord used for the method of the inventionshould be, as described above, a fibrous material for reinforcing thematrix of a structure. Synthetic fibers are particularly preferable.

In addition, with respect to the configuration of the fiber cord forreinforcement of the invention, as described above, it is preferablethat fiber cord is a single yarn or an assembly of several yarns. It isalso preferable that the fiber has been previously treated with an epoxyresin, a urethane resin, or the like in the stage of yarn-making orafter yarn making. Further, it is preferable that the fiber cord is atwisted cord. As described above, it is preferable that the fiber cordis obtained by aligning and twisting one or more fiber yarns (firsttwisting) and then aligning and twisting two or more such twisted yarns(second twisting).

The method for producing a fiber cord for reinforcement of the inventionis a method in which, first, such a fiber cord is treated with apre-treatment liquid. Here, the pre-treatment liquid contains a blockedisocyanate compound A₂ (hereinafter sometimes referred to as compoundA₂) and a blocked isocyanate compound B₂ (hereinafter sometimes referredto as compound B₂), and the content of the compound A₂ is lower than thecontent of the compound B₂. Further, here, it is preferable that theisocyanate group unblocking temperature of the compound A₂ is lower thanthe isocyanate group unblocking temperature of the compound B₂.

Here, a blocked polyisocyanate compound used in the method of theinvention is an addition reaction product between a polyisocyanatecompound and a blocking agent, which is the isocyanate protecting group.When heated, the blocked polyisocyanate compound releases the blockcomponent to produce an active polyisocyanate compound. In particular, apolyisocyanate containing terminal isocyanate groups obtained by areaction between isocyanate groups (—NCO) and hydroxyl groups (—OH) in amolar ratio of more than 1 exerts excellent performance and thus ispreferable. Examples of blocking agents include phenols such as phenol,thiophenol, cresol, and resorcinol, aromatic secondary amines such asdiphenylamine and xylidine, heterocyclic compounds such asdimethylpyrazole, α-dicarboxylic acids such as diethyl malonic acid,phthalic imides, lactams such as caprolactam and valerolactam, aliphaticcompounds such as acidic sodium sulfite, phenols such as phenol,thiophenol, cresol, and resorcinol, aromatic secondary amines such asdiphenylamine and xylidine, phthalic imides, lactams such as caprolactamand valerolactam, oximes such as acetoxime, methylethylketoxime, andcyclohexanone oxime, and acidic sodium sulfite.

Then, the blocked polyisocyanate compounds used in the method forproducing a fiber cord for reinforcement of the invention include bothof the blocked polyisocyanate compound A₂ blocked with an aromaticcompound or a compound containing an α-dicarboxylic acid component andthe blocked polyisocyanate compounds B₂ blocked with an aliphaticcompound or an alicyclic compound. It is still more preferable that theisocyanate group unblocking temperature of the compound A₂ is lower thanthe isocyanate group unblocking temperature of the compound B₂. Further,it is preferable that the unblocking temperature of the compound A₂ isless than 160° C., particularly within a range of 100 to 150° C.Meanwhile, it is preferable that the unblocking temperature of thecompound B₂ is 160° C. or more, particularly within a range of 160 to200° C. In addition, it is preferable that the abundance of the compoundA₂ is higher than the abundance of the compound B₂, and further it ispreferable that the solids weight ratio of compound A₂/compound B₂ is99/1 to 60/40.

Here, an unblocking temperature refers to a temperature at which theblocking group is released from a blocked isocyanate by heat, wherebythe isocyanate activity is developed. As preferred conditions for themethod of the invention, first, through the first-stage heat treatment,the blocked polyisocyanate compound A₂ blocked with an aromatic compoundor a compound containing an α-dicarboxylic acid component is unblockedand crosslinked. Then, through the subsequent second-stage heattreatment, the blocked polyisocyanate compound B₂ is unblocked, and thecompound-B₂-derived compound is crosslinked with the cross linkedisocyanate derived from the compound A₂. Further, it is preferable thatthe first-stage heat treatment is a low-temperature heat treatment, andthe second-stage heat treatment is a high-temperature heat treatment. Inthe method of the invention, crosslinking is performed in two stageslike this, whereby a tough, dense film of the pre-treatment liquid(first bath adhesive) can be formed inside and on the surface of thefiber cord. Accordingly, the fiber cord can be provided with enhancedfraying resistance, bending fatigue resistance, and adhesion. Inparticular, the obtained fiber cord is optimal for rubber reinforcementapplications, particularly for use as a cord for a transmission belt.

Here, with respect to the difference in unblocking temperature betweenthe compound A₂ and the compound B₂, the greater the better. It ispreferable that the difference in unblocking temperature between thecompounds A₂ and B₂[=(unblocking temperature of the compoundB₂)−(unblocking temperature of the compound A₂)] is 30° C. or more. Whenthe temperature difference is sufficient, the two-stage isocyanatecrosslinking reaction can take place more easily. When the temperaturedifference is too small, this results in a competing reaction, in whichthe crosslinking reactions of the compound A₂ and the compound B₂ takeplace at the same time. As a result, it tends to be difficult to controlthe crosslinked structure. In addition, this is likely to expose thedifference in the strength of the pre-treatment liquid film between theinner and outer layers of the fiber cord due to the difference in heatdistribution. In such a case, the fraying resistance and bending fatigueresistance tend to decrease. More specifically, as unblockingtemperatures, it is preferable that the unblocking temperature of thecompound A₂ is 110 to 130° C., and the unblocking temperature of thecompound B₂ is 160° C. to 180° C.

The compound A₂ used in the method of the invention is the abovecompound A₂ and has an isocyanate group blocked with an aromaticcompound or a compound containing an α-dicarboxylic acid component.Further, as the aromatic compound, a heterocyclic compound having acyclic structure containing nitrogen or like atoms in addition to carbonatoms is preferable, and it is particularly preferable that the aromaticcompound is a heterocyclic aromatic compound such as dimethylpyrazole(DMP). As the compound containing an α-dicarboxylic acid component, acompound blocked with diethyl malonate is preferable. Such a compound A₂is prone to having a resonance structure, allowing for unblocking at alower temperature.

In addition, the compound B₂ used in the method of the invention is theabove compound B₂ and has an isocyanate group blocked with an aliphaticcompound or an alicyclic compound. More specifically, those blocked withan oxime such as methylethylketoxime or a lactam such as ε-caprolactamare preferable.

In addition, the unblocking temperature is significantly affected by theblock-forming compound structure. In the method of the invention, it isparticularly preferable that the block structure of the compound A₂ is adimethylpyrazole (DMP) block structure, and the block structure of thecompound B₂ is an ε-caprolactam block structure.

In addition, in the invention, it is preferable that the blockedpolyisocyanate compound A₂ is composed of a compound having ahexamethylene diisocyanate (HDI) trimer structure represented by thefollowing chemical structural formula (I).

As shown in the above chemical structural formula (I), this blockedpolyisocyanate compound is a compound having, as its basic structure, atrimer structure in which three terminal NCO groups of the hexamethylenediisocyanate (HDI) form a cyclic structure. It is also preferable thateach trimer structure is, as shown in the following chemical structuralformula (II), for example, a condensed compound having further increasedfunctionality. Here, R of chemical structural formula (II) can beselected from polyglycols, such as polyethylene glycol, withoutimpairing the affinity for water and heat resistance.

In addition, in the invention, it is preferable that the blockedisocyanate compound A₂ is such that the number of functional groupspresent in the molecule after unblocking is three or more. In the casewhere the number of functional groups is two or less, the crosslinkingreactivity with the pre-treatment liquid and the reactivity to theadhesive treatment liquid tend to be insufficient. In particular, in thecase where the fiber cord for reinforcement of the invention is used forrubber reinforcement, such as a belt core material, aresorcin-formalin-latex (RFL)-based adhesive is usually used as theadhesive treatment liquid; however, there is a tendency that with thesmall amount of resorcinol-derived hydroxyl groups contained in RFLalone, the reactivity is likely to be insufficient.

Meanwhile, as the blocked polyisocyanate compound B₂, anε-caprolactam-blocked diphenylmethane diisocyanate (MDI) compound isparticularly preferable. In the invention, an epoxy compound and aflexible blocked polyisocyanate compound A₂ are crosslinked through thefirst-stage heat treatment, and then a blocked polyisocyanate compoundB₂ having a rigid MDI structure is further crosslinked through thesecond-stage heat treatment. As a result, a pre-treatment liquid film,which is particularly firm, dense, and also flexible, is formed insideand also on the surface layer of the fiber cord. Then, it has becomepossible to achieve significant improvements in fraying resistance,bending fatigue resistance, and adhesion, which have been difficult toachieve by the conventional aqueous adhesive treatment.

In addition, in the method for producing a fiber cord for reinforcementof the invention, it is preferable that the pre-treatment liquidcontains an epoxy compound in addition to the above two kinds of blockedisocyanate compounds.

Here, as the epoxy compound used in the invention, a compound having atleast two epoxy groups in one molecule is preferable. In particular, acompound containing at least 2 g equivalents of epoxy groups per kg ofcompound is preferable. More specifically, examples thereof includereaction products between a polyalcohol such as ethylene glycol,glycerol, sorbitol, pentaerythritol, or polyethylene glycol and ahalogen-containing epoxide such as epichlorohydrin; reaction productsbetween a polyphenol such as resorcin,bis(4-hydroxyphenyl)dimethylmethane, a phenol-formaldehyde resin, or aresorcin-formaldehyde resin and a halogen-containing epoxide asdescribed above; and polyepoxide compounds prepared by oxidizing anunsaturated compound with peracetic acid, hydrogen peroxide, or thelike, that is, 3,4-epoxycyclohexene epoxide,3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexene carboxylate,bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, and the like. Amongthem, a reaction product between a polyalcohol and epichlorohydrin, thatis, a polyglycidyl ether compound of a polyalcohol, develops excellentperformance and thus is particularly preferable.

In addition, it is also preferable that latexes and like components areused with and contained in the pre-treatment liquid used in theinvention.

In addition, in the method of the invention, it is preferable that thefiber cord is a fiber cord including a twisted fiber. When the fibercord is twisted, the pre-treatment liquid penetrates into the fiber cordmore effectively. In addition, it is preferable that the pre-treatmentliquid also contains an epoxy compound in addition to the two kinds ofblocked polyisocyanate compounds. When an epoxy compound is usedtogether with the two kinds of blocked polyisocyanate compounds, theeffect of the unblocking temperature difference between the two kinds ofblocked isocyanate compounds is exerted more clearly.

The blocked polyisocyanate compounds used in the invention have highaffinity for the fiber-forming polymer and have excellent penetrationand cohesive strength. Further, in order to promote the adhesion to thefiber surface and the polyisocyanate crosslinking reaction and obtain afirm adhesive film, it is preferable to use an epoxy compound together.Further, in the case where an epoxy compound is used together with thepre-treatment liquid of the invention like this, it is preferable thatthe epoxy compound is used such that the solids weight ratio of epoxycompound/blocked polyisocyanate compounds is 5/95 to 30/70, morepreferably 10/90 to 25/75, particularly 15/85 to 25/75.

In the case where an epoxy compound is used together, in the stage wherewater is distilled from the attached fiber and a heat treatment isperformed, the epoxy compound and the blocked polyisocyanate compoundsare thermally diffused into the fiber cord over a sufficient period oftime, and then the two kinds of blocking agents are released, causing acrosslinking reaction. As a result, high interface reinforceability isobtained. At the time of this thermal diffusion, it is preferable thatthe epoxy compound and the blocked polyisocyanate compounds arelow-molecular-weight components having high reaction activity.Accordingly, it is preferable that the pre-treatment liquid does notcontain a hydroxyl group or alkali component which crosslinks the epoxycompound or blocked polyisocyanate compounds or deactivates them withwater.

Here, with respect to the solids weight ratio of epoxy compound/blockedpolyisocyanate compounds, in the case where the compositional proportionof epoxy is too low, the curing reaction rate of the isocyanatecompounds tends to decrease. Thus, a firm crosslinked film is lesslikely to be obtained, and the fraying resistance is less likely to beimproved. Meanwhile, in the case where the compositional proportion ofthe epoxy compound is excessive, the crosslinked film tends to be hardand brittle. Accordingly, the bending fatigue resistance and durabilityare less likely to be improved.

In the invention, in the case where the above epoxy compound and blockedisocyanate compounds are used together, it is preferable that thepre-treatment liquid (first adhesive treatment agent) is a waterdispersion. Specifically, it is preferable to use a water dispersioncontaining them at a solids concentration of 2 to 20 wt %, morepreferably 5 to 15 wt %, at the time of application to the fiber.

In the method of the invention, for the application of such a waterdispersion (pre-treatment liquid) to the fiber, it is possible to employtechniques such as contact with a roller, application by spraying from anozzle, or immersion in a solution. In addition, it is preferable thatthe amount of solids of the pre-treatment liquid attached to the fiberis within a range of 0.5 to 5.0 wt %. When the amount attached is toosmall, the filaments forming the fiber cord cannot be sufficientlybundled, resulting in a decrease in fraying resistance. In particular,in the case where the fiber cord for reinforcement of the invention isused as a belt core material, it tends to be difficult to obtain asufficient and uniform pre-treatment liquid film for protecting thefiber interface from rubber vulcanization at the time of shaping a beltor aminolysis at the time of using the belt. Meanwhile, in the casewhere the amount attached is too large, there is a tendency thatgumming-up or the like occurs in the subsequent adhesive treatment stepor shaping step, resulting in a decrease in process passing properties.Therefore, it is preferable that the amount of solids of thepre-treatment liquid attached to the fiber is 0.5 to 5.0 wt %, stillmore preferably 1.0 to 3.0 wt %. The amount of solids attached can becontrolled by techniques such as squeezing with a pressure-weldingroller, scraping off with a scraper or the like, blowing off by airblowing, suction, or a beater. In order to increase the amount attached,attachment may be performed several times.

In the method of the invention, the pre-treatment liquid is applied tothe fiber cord, followed by a heat treatment. Here, as preferred heattreatment conditions, two-stage heating is preferable. Specifically, forexample, it is preferable that drying is performed at a temperature of80 to 150° C. for 60 to 120 seconds, and then a heat treatment isperformed at a temperature of 180 to 240° C. for 60 to 180 seconds.

That is, first, through the first-stage heat treatment, moisture on thecord surface and inside the cord is distilled off, and the pre-treatmentliquid containing blocked polyisocyanate compounds are thermallydiffused into the fiber cord at the same time. In the case where thetreatment condition is such that the temperature is low or the time isshort, moisture tends to remain not-distilled off. Accordingly, there isa tendency that the isocyanate compounds and the like are deactivated inthe subsequent high-temperature heat treatment, making it impossible toobtain a firm crosslinked film. On the other hand, in the case where thefirst-stage heat treatment is a high-temperature treatment, thecrosslinking reaction of the isocyanate compounds and the like takesplace as a competing reaction with hydrolysis, and thus the film tendsto be brittle. Further, there is a tendency that the remaining moisturein the fiber cord undergoes bumping, whereby the penetration of thepre-treatment liquid (first adhesive treatment agent) into the fibercord is inhibited. In addition, in the case where the heat treatmenttime is long, there is a tendency that the isocyanate compounds areair-oxidized, and the film performance decreases. As the conditions forthe first-stage heat treatment, it is more preferable that the treatmentis performed at a temperature of 90 to 120° C. for 60 to 120 seconds.

It is preferable that following this first-stage heat treatment (dryingheat treatment), a second-stage heat treatment is performed at atemperature of 180 to 240° C. for 60 to 180 seconds. As a result, thecrosslinking reaction takes place in the state where moisture has beensufficiently distilled from the fiber cord and the blockedpolyisocyanate compounds and the like have uniformly permeated into thefiber cord. In the case of a low-temperature treatment or a short-timetreatment, there is a tendency that the crosslinking reaction does notsufficiently progress, and the film is likely to be brittle. On theother hand, in the case of a high-temperature treatment or a long-timetreatment, there is a tendency that the isocyanate compounds and thelike are pyrolyzed or air-oxidized, making it difficult to exert theperformance. As the conditions for the second-stage heat treatment, itis more preferable that the treatment is performed at a temperature of200 to 235° C. for 60 to 120 seconds.

In the method for producing a fiber cord for reinforcement of theinvention, as described above, a pre-treatment liquid (first adhesivetreatment agent) is attached to the fiber cord, then the fiber cordhaving attached thereto the pre-treatment liquid is once heat-treated,and subsequently an adhesive treatment liquid is attached thereto,followed by a drying treatment.

Here, the adhesive treatment liquid is to be suitably changed accordingto the matrix for which the fiber cord for reinforcement of theinvention is used. For example, in the case where the fiber cord is usedfor a rubber structure such as a belt, it is preferable to use aresorcin-formalin-latex (RFL)-based adhesive as the adhesive treatmentliquid (second adhesive treatment agent).

This RFL-based adhesive has the above composition. Those having aresorcin/formaldehyde molar ratio within a range of 1/0.6 to 1/8 arepreferably used, and various latexes are usable.

In addition, it is also preferable that a crosslinking agent is usedtogether with this resorcin-formalin-latex (RFL) -based adhesivetreatment agent to serve as a treatment agent, and examples thereofinclude amines, ethylene urea, and blocked polyisocyanate compounds.Among them, considering the temporal stability of the treatment agent,the interaction with the pre-treatment agent, and the like, it ispreferable to use a blocked polyisocyanate compound. It is preferablethat the proportion of the crosslinking agent added is within a range of0.5 to 40 wt % relative to the RFL component. This is because althoughan increase in the amount added usually improves the adhesion strength,when the amount added is too large, conversely, there is a tendency thatthe compatibility of the adhesive with rubbers decreases, resulting in adecrease in adhesion strength to rubbers.

In the invention, it is preferable that an adhesive liquid (secondadhesive treatment agent) is used as a treatment liquid composed of awater dispersion, and that the total solids concentration of the waterdispersion is within a range of 5 to 30 wt %. In the case where thetotal solids concentration of the treatment liquid is lower than theabove range, the surface tension of the adhesive increases, and theadhesion to the fiber surface becomes less uniform. At the same time,with a decrease in the amount of solids attached, the adhesion tends todecrease. On the other hand, in the case where the total solidsconcentration is higher than the above range, the viscosity of thetreatment agent increases. Thus, there is a tendency that the amount ofsolids attached becomes too large, resulting in a decrease in processpassing properties, such as gumming-up in the adhesive treatment step orshaping step.

In order to attach the adhesive treatment liquid (second adhesivetreatment agent) to the fiber like this, it is possible to employtechniques such as contact with a roller, application by spraying from anozzle, or immersion in a solution. In addition, it is preferable thatthe amount of solids attached to the fiber cord is within a range of 1.0to 10.0 wt %, still more preferably within a range of 1.5 to 8.0 wt %.The amount of solids attached to the fiber cord can be controlled,similarly to the above, by techniques such as squeezing with apressure-welding roller, scraping off with a scraper or the like,blowing off by air blowing, suction, or a beater. In order to increasethe amount attached, attachment may be performed several times.

In the method of the invention, the adhesive treatment liquid isattached to the fiber cord and dried. As the heat treatment conditionsfor drying, it is preferable that the drying heat treatment is performedin two or more stages at a temperature of 100° C. to 250° C. for 60 to240 seconds. It is more preferable that drying is performed in atemperature range of 120 to 180° C. for 60 to 180 seconds, and then aheat treatment is performed at a temperature of 200 to 245° C. for 60 to180 seconds. When this drying/heat treatment temperatures are too low,the adhesion to rubbers tends to be insufficient, while when thedrying/heat treatment temperatures are too high, there is tendency thatthe air oxidation of the adhesive components at high temperatures ispromoted, resulting in a decrease in adhesion activity.

In the method for producing a fiber cord for reinforcement of theinvention, unlike the conventional solvent treatments, theorganic-solvent-based adhesive treatment formulation using an isocyanatecompound having free isocyanate groups is not employed. Accordingly,this production method is safe for the working environment and has areduced environmental impact. Then, a pre-treatment liquid that easilypenetrates into the fiber cord is applied preferably as a water-basedadhesive treatment agent, that is, a water dispersion, and two kinds ofblocked polyisocyanate compounds are successively unblocked, therebycausing a curing reaction while suppressing deactivation, whereby afirm, flexible crosslinked film is formed. The invention enhances theinterface adhesion strength between the fiber surface layer and thefiber inner layer impregnated with the pre-treatment liquid (firstadhesive treatment agent layer), as well as between the fiber innerlayer (first adhesive treatment agent layer) and the adhesive layer(second adhesive treatment agent layer). As a result, it has becomepossible to achieve improvements in both fraying resistance and bendingfatigue resistance, while ensuring high adhesion.

EXAMPLES

Hereinafter, the invention will be described with reference to examples.However, these examples are provided by way of illustration and do notlimit the invention. Incidentally, evaluations in the examples of theinvention were made according to the following measurement methods.

(1) Measurement of Compound Proportions in Fiber Cord Inner Layer Part(Pyrolysis GC-MS)

From an obtained fiber cord for reinforcement, the adhesive layer(outermost layer part) was peeled off to give a fiber cord having fibersexposed to the surface. Further, the outside quarter of the fiber cordwas trimmed off. From the inner layer part whose diameter is 75% of theoriginal fiber cord diameter, a measurement sample weighing 5 mg wascollected.

Using this sample, the compound proportions (weight ratio) weredetermined from the peak areas of the compound A₁ and the compound B₁ bya cut & weight method using a pyrolyzer (manufactured by JapanAnalytical Industry Co., Ltd., Curie Point Pyrolyzer “CCP JHP-5”) and agas chromatograph mass spectrometer (manufactured by ShimadzuCorporation Co., Ltd., “GC-MS QP2010”).

(Measurement Conditions) CCP (Pyrolyzer)

Oven temperature; 250° C., Needle temperature; 250° C., Sample heating;590° C.×15 sec

GC (Gas Chromatograph)

Vaporizing chamber temperature; 250° C., Column; DB-5 ms, Split ratio;1/100,

Column open program; 60° C.×2 min, heated at a temperature rise rate of10° C./min to 180° C. or 320° C.

MS (Mass Spectrometer)

Ion source temperature; 200° C., Interface temperature; 250° C., Massrange; 29 to 600

(2) Unblocking Temperature of Blocked Polyisocyanate

Using a thermobalance (TG/DTA, manufactured by Rigaku InternationalCorporation, “TAS-200”), 10 mg of a blocked polyisocyanate, from whichwater had been distilled, was heated in a nitrogen atmosphere from roomtemperature at a temperature rise rate of 10° C./min. The temperature atwhich the weight of the sample was reduced by 10 wt % was defined as theunblocking temperature.

(3) Tensile Strength, Breaking Elongation, 150-N Load Elongation(Intermediate Elongation), and 150° C. Dry Heat Shrinkage of Cord

Each was determined by measurement in accordance with JIS L1017.

(4) Cord Hardness

Measurement was performed using a Gurley hardness tester (manufacturedby Tester Sangyo Co., Ltd.) in accordance with JIS L1096-6.20.

(5) Peel Adhesion of Cord

This shows the peel adhesion between an adhesive-treated fiber cord anda rubber. Seven cords were embedded in the surface layer of asulfur-based EPDM rubber unvulcanized sheet, followed by vulcanizationat a temperature of 150° C. for 30 minutes under a pressing pressure of90 kg/cm². Next, every other one of the cords from both ends, four cordsin total, were removed, and the remaining three cords weresimultaneously peeled from the rubber sheet at a rate of 200 mm/min. Theforces required for peeling (N/3 cords) were averaged to determine thepeel adhesion per cord (N/cord).

(6) Bending Fatigue Resistance and Fraying Resistance of Cord

Eight adhesive-treated fiber cords were embedded at regular intervals intwo unvulcanized rubber sheets of sulfur-based EPDM rubber (50 mm inwidth, 500 mm in length, and 2 mm in thickness), followed byvulcanization at a temperature of 150° C. for 30 minutes under apressing pressure of 50 kg/cm², thereby giving a belt-like rubber shapedarticle. Next, while applying a load of 30 kg, the belt-like rubbershaped article was installed on a roller 20 mm in diameter, andsubjected to back-and-forth movements at 100 rpm in an atmosphere at100° C. for a roller bending (contact) distance of 100 mm. Afterrepeating bending 10,000 times, the cords were taken out, and theremaining strength was measured to determine the strength retentionafter bending fatigue. In addition, after the bending fatigue, thebelt-like rubber shaped body was cut in the direction perpendicular tothe embedded fiber cords, and the bundling conditions of the fiber cordsexposed to the cross-section were observed visually and also under anoptical microscope to evaluate fraying resistance. The frayingresistance was rated in the following three grades.

[Fraying Resistance (after Bending Fatigue Test)]

5: The filaments of the fiber cords are bundled, and no abnormalitiesare seen in the appearance; excellent. 3: Some filaments of the fibercords have slight bundling failures; however, good.

1: The filaments of the fiber cords have bundling failures and are notbundled.

Example 1

To 22.8 g of a polyepoxide compound having a sorbitol polyglycidyl etherstructure (“Denacol EX-614B” manufactured by Nagase ChemteX Corporation;concentration: 100%) was added 8.8 g of an aqueous dialkylsulfosuccinate sodium salt solution (“Neocol SW-C” manufactured by DKSCo., Ltd.; concentration: 70%) as a surfactant, followed by stirring,and the mixture was added to 723.7 g of water with stirring anddissolved. Then, 226.5 g of a dimethylpyrazole block-HDI trimmercondensate having three or more functional groups (“Trixene 327”manufactured by Baxenden (UK); unblocking temperature: 115° C.,concentration: 38%) as a blocked polyisocyanate compound A₂ (shows as“a” in Table 1) and 18.2 g of a bifunctional c-caprolactam-blockeddiphenylmethane diisocyanate (“GRILBOND IL-6” manufactured by EMS;unblocking temperature: 170° C., concentration: 50%) as a blockedpolyisocyanate compound B₂ (shown as “b” in Table 1) were added theretowith stirring, thereby preparing a pre-treatment liquid (waterdispersion of a first adhesive treatment agent, solids concentration:12%), wherein the solids weight ratio of epoxy compound/blockedpolyisocyanate compounds (the total of the blocked polyisocyanatecompound A₂ and the blocked polyisocyanate compound B₂) was 20/80, andthe solids weight ratio of blocked polyisocyanate compound A₂/blockedpolyisocyanate compound B₂ was 90/10.

19.8 g of a resorcin-formalin initial condensate having aresorcin/formalin (R/F) molar ratio of 1/0.6 (“Sumikanol 700S”manufactured by Sumitomo Chemical Co., Ltd.; concentration: 65%) wasdissolved in an aqueous alkali solution prepared by adding 5.0 g of 10%caustic soda and 19.9 g of 20% ammonia water to 154.5 g of water, andthen 138.3 g of a vinylpyridine-styrene-butadiene latex (“Pyratex”manufactured by Nippon A&L Inc.; concentration: 41%), 206.2 g of apolybutadiene latex (“Nippol LX111NF” manufactured by Zeon Corporation;concentration: 55%), and 363.6 g of water were added thereto. 16.8 g of37% formalin water and 75.9 g of a methylethylketoxime-blockeddiphenylmethane diisocyanate (“DM6400” manufactured by Meisei ChemicalWorks, Ltd.; concentration: 40%) were added to this mixture, followed byaging at 20° C. for 48 hours, thereby preparing an adhesive treatmentliquid having a solids concentration of 22% (RFL-based second adhesivetreatment agent for second treatment bath).

Two polyethylene terephthalate untreated fibers of 1,100 dtex/192 fil(“P904B” manufactured by Teijin Fibers) were first-twisted in theS-direction (number of twists: 220/m), and then three of thefirst-twisted cords were second-twisted in the Z-direction (number oftwists: 120/m), thereby giving a polyester fiber cord. UsingComputreater (dip cord treater manufactured by C.A. Litzler), this fibercord was fed at a rate of 22 m/min and immersed in the pre-treatmentliquid (first adhesive treatment agent), then dried at a fixed length at120° C. for 60 seconds, and heat-treated at a fixed length at 235° C.for 60 seconds. Subsequently, the cord was immersed in the adhesivetreatment liquid (second treatment bath), then dried at a fixed lengthat 160° C. for 120 seconds, and heat-treated under 3.5% stretchingconditions at 230° C. for 150 seconds, thereby giving a polyester(polyethylene terephthalate) adhesive-treated fiber cord. Thisadhesive-treated fiber cord had attached thereto the pre-treatmentliquid (first-bath adhesive treatment agent) and adhesive treatmentliquid (second-bath adhesive treatment agent) in amounts of 2.6 wt % and4.8 wt %, respectively, relative to the weight of the polyester fibercord on a solids basis.

The compound proportions in the inner layer part of the obtained fibercord were measured (pyrolysis GC-MS). As a result, the ratio of thecompound A₁ derived from dimethylpyrazole (DMP) and the compound B₁derived from ε-caprolactam were as follows: A₁/B₁=80/20. The performanceevaluation results of the obtained fiber cord are collectively shown inTable 1.

Examples 2, 3, and 4, Comparative Example 1

Polyester fiber cords were subjected to an adhesive treatment in thesame manner as in Example 1, except that the solids weight ratio ofblocked polyisocyanate compound A₂/blocked polyisocyanate compound B₂ inthe pre-treatment liquid (first adhesive treatment agent) of 90/10 inExample was changed as shown in Table 1 in preparation. The performanceevaluation results of the obtained polyester adhesive-treated fibercords are collectively shown in Table 1.

Comparative Example 2

A polyester fiber cord was subjected to an adhesive treatment in thesame manner as in Example 1, except that in the pre-treatment liquid(first adhesive treatment agent), only the blocked polyisocyanatecompound A₂ was used, and the blocked polyisocyanate compound B₂ was notused. The performance evaluation results of the obtained polyesteradhesive-treated fiber cord are collectively shown in Table 1.

TABLE 1 Comparative Comparative Example 1 Example 2 Example 3 Example 4Example 1 Example2 Pre-Treatment Liquid Compound A₂ a a a a — a CompoundB₂ b b b b b — A₂/B₂ Ratio 90/10 99/1 70/30 50/50 0/100 100/0 PhysicalProperties of Compound A₁/Compound B₁ Ratio 80/20 94/6 65/35 55/45 0/100100/0 Fiber Cord for Strength (N) 380 382 389 381 392 386 ReinforcementBreaking Elongation (%) 19.2 19.1 20.0 20.8 22.6 23.1 150-N LoadElongation (%) 8.5 8.5 8.6 8.7 9.5 8.6 150° C. Dry Heat Shrinkage (%)2.1 2.1 2.1 2.1 1.9 1.9 Cord Hardness (mg) 44,800 28,100 36,200 28,50021,600 30,600 Peel Adhesion (N/cord) 29.4 26.9 27.8 23.5 22.7 24.2Strength Retention after Bending 94 96 92 84 79 71 Fatigue (%) FrayingResistance 5 5 5 3 1 1 a; Dimethylpyrazole block-HDI trimmer condensateb; ε-Caprolactam-blocked diphenylmethane diisocyanate

Examples 5, 6, and 7

Polyester fiber cords were subjected to an adhesive treatment in thesame manner as in Example 1, except that the solids weight ratio ofepoxy compound/blocked polyisocyanate compounds (total amount) in thepre-treatment liquid (first adhesive treatment agent) of 20/80 inExample 1 was changed as shown in Table 2 in preparation. Theperformance evaluation results of the obtained polyesteradhesive-treated fiber cords are collectively shown in Table 2.

Example 8

A polyester fiber cord was subjected to an adhesive treatment in thesame manner as in Example 1, except that in the pre-treatment liquid(first adhesive treatment agent), the blocked polyisocyanate compound A₂was changed from the dimethylpyrazole block-HDI trimmer condensate usedin Example 1 to a diethyl malonate-HDI trimmer condensate having threeor more functional groups (unblocking temperature: 120° C.,concentration: 25%) (shown as in Table 2). The performance evaluationresults of the obtained polyester adhesive-treated fiber cord arecollectively shown in Table 2.

Example 9

A polyester fiber cord was subjected to an adhesive treatment in thesame manner as in Example 1, except that in the adhesive treatmentliquid (RFL-based second adhesive treatment agent for second treatmentbath), 138.3 g of VpSBR (concentration: 41%) in thevinylpyridine-styrene-butadiene latex (VpSBR) and polybutadiene latex(PB) in Example 1 was replaced with 127.5 g of a chlorosulfonatedpolyethylene (CSM) latex (Sepolex CSM, manufactured by Sumitomo SeikaChemicals Co., Ltd.; concentration: 40%) (L1). The performanceevaluation results of the obtained polyester adhesive-treated fiber cordare collectively shown in Table 2.

TABLE 2 Example 1 Example 5 Example 6 Example 7 Example 8 Example 9Pre-Treatment Liquid Compound A₂ a a a a a′ a Compound B₂ b b b b b bA₂/B₂ Ratio 90/10 90/10 90/10 90/10 90/10 90/10 Epoxy/(A₂ + B₂) Ratio20/80 10/90  5/95 30/70 20/80 20/80 Adhesive Treatment Latex ComponentVp/BP Vp/BP Vp/BP Vp/BP Vp/BP CSM/BP Liquid Physical Properties ofCompound A₁/Compound B₁ Ratio 80/20 80/20 80/20 80/20 80/20 80/20 FiberCord for Strength (N) 380 386 375 381 381 382 Reinforcement BreakingElongation (%) 19.2 19.7 18.7 19.0 18.4 19.1 150-N Load Elongation (%)8.5 8.5 8.4 8.3 8.2 8.5 150° C. Dry Heat Shrinkage (%) 2.1 2.1 2.1 2.22.2 2.0 Cord Hardness (mg) 44,800 41,500 38,100 40,800 40,800 44,100Peel Adhesion (N/cord) 29.4 28.3 26.0 26.4 27.9 29.2 Strength Retentionafter Bending 94 93 96 80 92 95 Fatigue (%) Fraying Resistance 5 5 5 5 55 a; Dimethylpyrazole block-HDI trimmer condensate a′; Diethylmalonate-HDI trimmer condensate b; ε-Caprolactam-blocked diphenylmethanediisocyanate Vp; VpSBR latex CSM; CSM latex BP; BP latex

In Examples 1 to 9 of the invention, as compared with comparativeexamples, the cords had high hardness and excellent bending fatigueresistance, and the fraying resistance after bending fatigue was alsoexcellent. In addition, in the examples, the cord strength and breakingelongation tended to be lower as compared with the comparative exampleshaving poor bundling properties; this is considered to be the influenceof an increase in bundling properties caused by the formation of a firmfilm due to the penetration of the pre-treatment liquid (first adhesivetreatment agent) into the fiber cord. However, the strength retentionafter bending fatigue of each fiber cord is high, and also the modulus(intermediate elongation) and dry heat shrinkage, which are important asa belt cord, are maintained at values indicating sufficient performance.

However, in the case where the proportion of, among the blockedisocyanate compounds in the pre-treatment liquid, the rigidhigh-temperature-dissociation blocked isocyanate compound B₂ is high asin Example 4, or in the case where the proportion of the epoxy compoundin the pre-treatment liquid is high as in Example 7, there is a tendencythat the adhesion film is slightly weak, resulting in slight decreasesin cord hardness, fraying resistance, and adhesion.

In addition, in Comparative Example 1, only a bifunctionalhigh-temperature-dissociation diisocyanate compound B₂ was used as ablocked isocyanate compound. As a result, the cord hardness, frayingresistance, adhesion, and bending fatigue resistance were all lower ascompared with the examples.

INDUSTRIAL APPLICABILITY

According to the invention, a fiber cord for reinforcement havingsignificantly improved fraying resistance and being excellent inadhesion to rubbers, bending fatigue resistance, and durability isobtained. In particular, the fiber cord for reinforcement of theinvention is suitable for rubber reinforcement, particularly as atransmission belt cord. The fiber cord is particularly optimal forautomobiles, where weight reduction is required. In addition, in themethod of the invention, water-based adhesive treatments can also beemployed. Thus, as an environment-conscious method for producing anadhesive-treated fiber cord, the method can be significantly effectivein reducing the environmental impact and cost.

1. A fiber cord for reinforcement, comprising an adhesive treatmentagent attached to a surface thereof, characterized in that the fibercord includes, in an inner layer part thereof, a compound A₁ having amolecular weight of less than 1,000 and a smaller amount of a compoundB₁ than the compound A₁, the compound A₁ being an aromatic compound or acompound containing an α-dicarboxylic acid component, the compound B₁being an aliphatic compound or an alicyclic compound.
 2. The fiber cordfor reinforcement according to claim 1, wherein the adhesive treatmentagent is a resorcin-formalin-latex (RFL)-based adhesive.
 3. The fibercord for reinforcement according to claim 1, wherein the fiber cordincludes a twisted multifilament fiber.
 4. The fiber cord forreinforcement according to claim 1, wherein the fiber cord includes asynthetic fiber.
 5. The fiber cord for reinforcement according to claim1, wherein the aromatic compound is a heterocyclic compound.
 6. Thefiber cord for reinforcement according to claim 1, wherein the compoundA₁ is located only in the inner layer part of the fiber cord.
 7. Thefiber cord for reinforcement according to claim 1, wherein a compoundhaving a hexamethylene diisocyanate (HDI) trimer structure is present inthe inner layer part of the fiber cord.
 8. The fiber cord forreinforcement according to claim 1, wherein no latex is present in theinner layer part of the fiber cord.
 9. A method for producing a fibercord for reinforcement, including treating a fiber cord in two stageswith a pre-treatment liquid and an adhesive treatment liquid, the methodbeing characterized in that the pre-treatment liquid contains two kindsof blocked isocyanate compounds that are a compound A₂ and a smalleramount of a compound B₂, the compound A₂ having an isocyanate groupblocked with an aromatic compound or a compound containing anα-dicarboxylic acid component, the compound B₂ having an isocyanategroup blocked with an aliphatic compound or an alicyclic compound, and afiber cord having the pre-treatment liquid attached thereto is oncesubjected to a heat treatment, and then the adhesive treatment liquid isattached thereto, followed by a drying treatment.
 10. The method forproducing a fiber cord for reinforcement according to claim 9, whereinthe aromatic compound is a heterocyclic compound.
 11. The method forproducing a fiber cord for reinforcement according to claim 9, whereinthe unblocking temperature of the compound A₂ is lower than theunblocking temperature of the compound B₂.
 12. The method for producinga fiber cord for reinforcement according to claim 9, wherein thecompound A₂ has a hexamethylene diisocyanate (HDI) trimer structure. 13.The method for producing a fiber cord for reinforcement according toclaim 9, wherein the compound B₂ has an isocyanate group blocked with analiphatic compound or an alicyclic compound.
 14. The fiber cord forreinforcement according to claim 2, wherein the fiber cord includes atwisted multifilament fiber.
 15. The method for producing a fiber cordfor reinforcement according to claim 10, wherein the unblockingtemperature of the compound A₂ is lower than the unblocking temperatureof the compound B₂.